The invention relates to a semiconductor structure and to a method for fabricating such a structure, and in particular a DMOS/IGBT structure.
DMOS transistors and IGBT (Insulated Gate Bipolar Transistor) transistors are known electronic components which are employed in a multiplicity of components appertaining to electronics. One important characteristic quantity of such components is their on resistivity Ron*A (Ron=on resistance; A=cross-sectional area of the resistance). The latter should be kept as low as possible since a low on resistivity entails low static power losses and also high current densities. The on resistivity is substantially influenced by the thickness of the semiconductor substrates (carrier substrates) of the DMOS/IGBT components. Thus, in new generations of vertical DMOS transistors, the proportion of the total on resistivity that is brought about by the semiconductor substrate amounts to approximately ¼. Therefore, attempts are made to keep the thickness of the semiconductor substrate as thin as possible, which is effected, for example by thinning by grinding processes at the underside of the semiconductor substrate after a structure comprising further semiconductor layers and metal layers has been applied/impressed on/in the top side of the semiconductor substrate.
In the previous fabrication methods, the thickness of the semiconductor substrate for DMOS components can be reduced to the order of magnitude of 100 μm. In the case of IGBTs and diodes, it is even possible to achieve somewhat smaller semiconductor substrate thicknesses. What is problematical, however, is that losses of yield may occur relatively frequently on account of broken substrates or cracks which arise as a result of strains or warpage of the semiconductor substrate on account of the thinning by grinding processes.
Therefore, the object on which the invention is based is to specify a semiconductor structure by means of which the losses of yield are avoided as far as possible, without having to dispense with the advantages of a thin semiconductor substrate; moreover, the intention is to provide a fabrication method suitable for this.